A wide variety of coatings have been used to coat the surfaces of packaging articles (e.g., food and beverage cans). For example, metal cans are sometimes coated using “coil coating” or “sheet coating” operations, i.e., a planar coil or sheet of a suitable substrate (e.g., steel or aluminum metal) is coated with a suitable composition and hardened (e.g., cured). The coated substrate then is formed into the can end or body. Alternatively, liquid coating compositions may be applied (e.g., by spraying, dipping, rolling, etc.) to the formed or partially formed article and then hardened (e.g., cured).
Packaging coatings should preferably be capable of high-speed application to the substrate and provide the necessary properties when hardened to perform in this demanding end use. For example, the coating should be safe for food contact, have excellent adhesion to the substrate, have sufficient flexibility to withstand deflection of the underlying substrate without rupturing (e.g., during fabrication steps and/or damage occurring during transport or use of the packaging article), and resist degradation over long periods of time, even when exposed to harsh environments.
Many current packaging coatings contain mobile or bound bisphenol A (“BPA”) or aromatic glycidyl ether compounds, polyvinyl chloride (“PVC”), or styrene. Although the balance of scientific evidence available to date indicates that the small trace amounts of these compounds that might be released from existing coatings does not pose any health risks to humans, these compounds are nevertheless perceived by some people as being potentially harmful to human health. From the foregoing, it will be appreciated that what is needed in the art is a packaging container (e.g., a food or beverage can or a portion thereof) that is coated with a composition that does not contain extractable quantities of such compounds.